Apparatus and method for conversion of hydrocarbons

ABSTRACT

An apparatus and method for effecting fluid catalytic cracking of hydrocarbons to products boiling in the gasoline range including a seal well containing a pressure-developing column of regenerated catalyst for transfer of the catalyst through a reaction zone, the seal well being in open pressure communication with the outlet of the reaction zone.

United States Patent [561 References Cited UNITED STATES PATENTS [72]Inventor Robert W. Pieiffer Bronxville,N.Y.

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Primary ExaminerHerbert Levine Attorneys-John C. Quinlan and MargaretaLe Maire [54] APPARATUS AND METHOD FOR CONVERSION OF HYDROCARBONS 25Clalms, 5 Drawlng Figs.

ABSTRACT: An apparatus and method for effecting fluid catalytic crackingof hydrocarbons to products boiling in the [50] Field of nvonocmaorqFEED 2a STEAM 22 PATENTEU SEPZI um SHEET 2 UP 2 2 M R. 7 HR 3 .nm, flm 9EN N E 7 E RM W .0 6 T A 8 TI T B m m 79 FIG.4

21 STEAM 774 FIG.5

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HYDROCARBON FEED 73 APPARATUS AND METHOD FOR CONVERSION OF HYDROCARBONSThis application is a continuation-in-part of pending application Ser.No. 719,052, filed Apr. 5, 1968 now U.S. Pat. No. 3,492,221.

The present invention relates to an apparatus and a method forconversion of hydrocarbons and more specifically to an apparatus andmethod for fluid catalytic cracking of relatively heavy hydrocarbons tohigh quality gasoline product.

In recent years, commercial catalytic cracking catalysts have beendeveloped which are highly active and also exhibit superior selectivitytowards the formation of desirable products such as gasoline at theexpense of coke and light ends production. Examples of such catalystsare those of the types commonly called high alumina and molecular sievecatalysts. It has been found that maximum benefit is derived from thesecatalysts by reducing the time the catalyst is in contact with thehydrocarbons undergoing cracking in the reaction zone. For this reason,it is preferred to carry out the catalytic cracking operations employingso-called dilute or disperse phase cracking techniques, i.e., thecatalyst is contacted with a hydrocarbon feed stream moving through thereaction zone at sufficiently high superficial velocities that thecatalyst is carried along in said stream as a dilute suspension and witha minimum of back-mixing.

In general, catalytic cracking of relatively high boiling hydrocarbonsto form substantial quantities of materials boiling in the gasolinerange is carried out in the following process sequence: hot regeneratedcatalyst is contacted with preheated hydrocarbon feed in a reaction zoneunder conditions suitable for cracking, the cracked hydrocarbon vaporsare disengaged from the spent catalyst, which is subsequently fed to astripping zone where it is contacted with a gasiform stripping agent,whereby volatile hydrocarbon material is stripped from the catalyst. Thestripped catalyst is then transferred to a regeneration zone where it isregenerated by burning carbonaceous deposits from the catalyst using anoxygen-containing gas such as air, after which the regenerated catalystis transferred to the reaction zone for reuse. The hydrocarbon materialfrom the reaction zone and the stripping zone is transferred to arecovery system including suitable fractionation equipment for recoveryof gaseous products, gasoline and one or more heavier fractions boilingabove the gasoline range. The latter fractions may be withdrawn asproducts of the process or may at least in part be recycled to thereaction zone for further cracking.

It has been found that substantial economies are realized when theregenerator vessel is superimposed in vertical alignment on a vesselcontaining the reaction zone, the catalyst disengaging zone and thestripping zone. One important advantage of such an arrangement is thatthe catalyst may be transferred from the regeneration zone into thereaction zone through a straight line vertical standpipe, and similarly,stripped catalyst can be introduced to the regenerator through astraight line vertical riser, thereby avoiding the erosion and/orfluidization problems heretofore resulting from the lateral transport ofdense phase catalyst.

Another important advantage of this arrangement is that the regenerationzone can be operated at a lower pressure than the reaction zone, andconsequently the cost of construction of the vessel as well as the costof compression of the oxygencontaining regeneration gas can beminimized. Moreover, due to the relatively higher pressure of thecracked hydrocarbon vapors, the size and cost of the fractionationequipment as well as the compression cost in handling normally gaseoushydrocarbons in the recovery system also are minimized.

There are, however, many problems connected with the design of a dilutephase reaction zone included in the aforementioned apparatus. It isnecessary that the vertical standpipe supplying freshly regeneratedcatalyst from the upper regeneration vessel to the inlet of the reactionzone, usually located in a lower portion of the lower vessel, be rigidlysup ported by either the upper vessel or by the top section of the lowervessel.

A design rigidly connecting the outlet of said standpipe with the inletto a dilute phase reaction zone conduit, where the latter is supportedby the bottom portion of the lower vessel, cannot be tolerated. This isso, because during startup of such a unit, the considerable downwardexpansion of the standpipe would result in mechanical failure of therigid connection between said reaction zone and the standpipe.

In copending application Ser. No. 719,052 an apparatus and a method aredisclosed, which solve the aforementioned problems. The method iscarried out in an apparatus having an upper regeneration vessel, a lowervessel, and a structure forming an open seal well within the lowervessel. A standpipe communicates with the upper vessel and the open sealfor transport of hot freshly regenerated catalyst to the seal well andvalve means are provided for controlling flow of catalyst through thestandpipe into the seal well. A confined elongated transfer-reactionzone located within the lower vessel depends from said seal well and isin open pressure communication therewith. In the seal well a sealing andpressure-developing fluidized dense bed of regenerated catalyst ismaintained and the thus developed pressure is employed for transferringcatalyst from said seal well through said transfer zone. Hydrocarbonfeed is introduced into the confined elongated transfer zone which ismaintained under conditions suitable for cracking of said hydrocarbons.Cracked hydrocarbons and spent catalyst are withdrawn from the transferzone and separated, the spent catalyst is stripped in a stripping zoneand then passed to the upper regeneration vessel where it isregenerated.

Although the above described apparatus and method have enjoyedconsiderable commercial success, these are instances when said apparatusand method are somewhat restricting as to the desired conversion orhydrocarbon feed throughputs. This is particularly so when an existingcommercial installation is to be revamped from a conventional dense bedcracking operation carried out in the lower vessel to short contact timedilute phase operations in transfer lines contained entirely within saidlower vessel.

The present invention is an improvement over the apparatus and method ofapplication Ser. No, 719,052, in that it provides for conversion ofhydrocarbons under conditions which are largely independent of anylimitations imposed by the size of the lower vessel. More specifically,the present invention enables hydrocarbons to be cracked employing anydesired contact times and hydrocarbon feed throughputs.

In accordance with the present invention the apparatus for theconversion of hydrocarbons comprises an upper vessel; a lower vessel; astructure forming an open seal well supported by said lower vessel; astandpipe in communication with the upper vessel and the open seal well;a confined elongated transfer zone depending from said seal well andpartially located outside said lower vessel and having the outletportion located within said lower vessel in open pressure communicationwith said seal well; valve means for controlling flow of solid materialthrough said standpipe into said seal well; means for introducinghydrocarbon feed into the confined elongated transfer zone; a solidsstripping zone; means for introducing solids from the transfer zone intosaid stripping zone, and means for transferring solids from the solidsstripping zone to the upper vessel.

In accordance with the present invention there is also provided a methodfor the conversion of hydrocarbons comprising transferring hot, freshlyregenerated catalyst of fluidizable particle size from an upperregeneration zone through a standpipe to an open seal well supported bya lower vessel, maintaining said open seal well in open pressurecommunication with the outlet of a confined elongated transfer zonedepending from said seal well and partially located outside the lowervessel, maintaining a sealing and pressure-developing dense bed offluidized, regenerated catalyst in said open sea] well; employing thethus developed pressure for transferring catalyst from said open sealwell through said depending confined elongated transfer zone,concurrently contacting in said transfer zone said catalyst withhydrocarbon feed under conditions suitable for cracking of saidhydrocarbon feed, withdrawing cracked hydrocarbons and spent catalystfrom the outlet portion of the transfer zone, stripping spent catalystof strippable hydrocarbons in a stripping zone, recovering cracked andstrippable hydrocarbons in a product recovery zone, and regeneratingstripped catalyst in the upper regeneration zone by contact with anoxygen-containing gas at temperatures above those employed in thetransfer zone.

The upper vessel may be of any design suitable for the regeneration ofspent catalyst employing fluidized dense bed techniques and shouldinclude means for introduction of oxygen-containing gas into a bottomportion of said vessel, and preferably cyclones located in an upperportion of said vessel for the recovery of entrained solids from theregenerator flue gases and return of said solids to the bed of catalystundergoing regeneration. The lower vessel, containing a portion of theconfined elongated transfer zone, may be provided with means formaintaining a fluidized dense bed of solid material in the bottomportion thereof, said means including inlets for fluidizing gases suchas steam, nitrogen or hydrocarbon feed. The lower vessel shouldpreferably be of a sufficient size to permit the installation ofcyclones in an upper portion thereof for the purpose of recoveringentrained solids from the vapors exiting the lower vessel. The strippingzone or zones can be provided by suitable partitions located within alower portion of the vessel or as a lesser diameter downward extensionof the lower vessel, or as a separate vessel.

Preferably both the upper and the lower vessels are of an essentiallycylindrical shape having spherical or semispherical heads. The uppervessel may be directly superimposed on the lower vessel providing aso-called single-head system, or it can be positioned above the lowervessel such that atmospheric air can circulate between the vesselsproviding what is commonly known as a two-head system. The single-headstructure is generally more economical in regard to systems in which thediameter of the regenerator is not more than about feet. Below suchdiameters, the amount of metal expansion incurred can be reasonablyaccommodated by using metal thicknesses in the vessel structure whichcan be fabricated and handled without excessive cost and withoutincurring unreliable vessel quality which may render the vesselunsuitable. At greater diameters than the above stated, a two-headsystem is preferably used.

In the single-head" system the support point of a suspended verticalstandpipe communicating with the upper and lower vessels is located inthe upper portion of the lower vessel, while in the two-head system asuspended standpipe may be supported in a lower portion of the uppervessel or may be supported in the upper portion of the lower vessel. Inthe latter system a seal between the standpipe and the lower vessel isprovided, e.g., by a bellows-type expansion joint which is requiredbetween the upper and lower vessels.

In a single-head" system it is possible to provide the section of thestandpipe extending from a lower portion of the upper vessel into anupper portion of the lower vessel with an annular space enveloping saidsection and means for introducing thereto a cooling gas such aslow-temperature steam. This arrangement will serve to protect the nozzlelocated in the common partition through which the standpipe extends,i.e., said nozzle can then be maintained at temperatures considerablylower than that of the upper vessel and that of the solids flowingthrough the vertical standpipe. Alternately, by employing a considerablylarger nozzle in the head, it is possible to provide sufficientinsulation thickness to protect the head from the high temperaturesolids flowing through the standpipe, and thus obviate the requirementfor the nozzle cooling gas.

The vertical standpipe is advantageously provided with means forintroduction of aeration gas at points spaced throughout the length ofthe standpipe to promote a smooth and steady flow of solidstherethrough.

The geometric configuration of the open seal well structure envelopingthis vertical standpipe is not too important as long as there issufficient space between the walls of the structure and the standpipe topermit a fluidized dense bed of solid material to be maintained in saidspace; for instance, a horizontal cross section thereof could be asquare, rectangle, ellipse, or of any other suitable shape. However, forease of construction and maintenance it is preferred that at least theupper portion of said well structure be of a generally cylindrical shapewith its longitudinal axis coinciding with that of the standpipe. It isnot necessary that the entire seal well structure be within the confinesof the lower vessel, and in some cases it might be desirable to extend alower portion of said structure downwards through the bottom of saidlower vessel. However, it is essential that the vapor outlet from saidseal well be located within the lower vessel. Fluidizing gas inlet meansare located in the lower portion of the seal well.

The first portion of the transfer zone immediately subsequent to theseal well and upstream from the hydrocarbon inlet is generally locatedmostly outside and below the lower vessel and provides for change offlow of dense phase fluidized material from downward to a substantiallyupward direction. It is preferably comprised of a section depending fromsaid seal well and extending downwardly therefrom, followed by either areturn bend or by a lesser bend and an upwardly sloped lateral section.said lesser bend is preferably a short radius bend, i.e., a bend havinga configuration such that the radius of curvature R of the bend isrelated to the diameter D of the pipe by the relationship R/kll).However, other bends may also be employed, e.g., having R/D=l .5.

It is required that the combined heights of the well structure and thesection extending downwardly from said well to the bend be at leastsufficient to maintain the above-mentioned fluidized dense bed of solidmaterial in said well such that it will develop sufficient pressure toenable circulation of solids at design rates through the transfer zonedepending from said well.

For the purpose of insuring operational stability, it is preferred thatthe first portion of the transfer zone is provided with a plurality ofmeans for introducing fluidizing gas to the section extending downwardlyfrom the seal well and also to the upwardly sloped lateral section,thereby assuring smooth downward flow of catalyst and providing for areverse seal consisting of a fluidized relatively dense bed of solids inthe upwardly sloped section of the first portion of the transfer zone.The hydrocarbon feed is introduced through one or more inlets located atsome distance downstream from said latter fluidizing gas inlets. in caseof a temporary pressure upset during the operation of the apparatus, theaforementioned reverse seal will prohibit the passage of vaporizinghydrocarbons into the seal well which otherwise might necessitate thediscontinuation of operations to reestablish the correct flow patterns.

At the aforementioned hydrocarbon feed inlets, there should bepreferably located means for introducing a dispersing medium such assteam. These will also be in use during startup of the apparatus to aidin establishing catalyst circulation prior to introduction ofhydrocarbon feed.

The valve means for control of solid material through the standpipecould be a slide valve in, for instance, the portion of the standpipelocated between the upper and the lower vessels in a two-head system.Another and more preferred alternative, which can be used in either thesingle or two-head system, is a plug valve which seats against the lowerend of the standpipe, said valve being vertically reciprocable through abushing in the bottom of the lower vessel. The total differentialmovement of the standpipe between its support point and the valve seatat its lower extremity, varies the hot and cold positions of the valveseat. This valve is controlled in such a manner that its opening willgive the desired flow rate regardless of the movements of its seat dueto expansion resulting from change in temperature.

In two-hea system designs using a slide valve for controlling the flowof solids in the vertical standpipe, the open seal well structure may besupported at an upper portion thereof by an adjacent portion of thestandpipe or alternatively at the lower vessel head. The preferredembodiment of the invention, whether a plug valve or slide valve isemployed for said purpose, includes the rigid support of the open sealwell structure by a bottom portion of the lower vessel.

The invention is not limited to one specific design of the elongatedconfined transfer zone which is depending from the seal well, the onlyrequirement being that the length and volume be sufi'icient to provideadequate contact between the hydrocarbon feed and the solid catalyst toresult in the desired conversion of the feed and that the transfer zonebe in open pressure communication with the seal well, i.e., the outletportion of the transfer zone and the vapor outlet from the seal wellmust be located in the same vessel. It is preferred however that asecond portion of the transfer zone immediately downstream from thehydrocarbon feed inlet be substantially vertical to provide forsubstantially vertical upflow conditions therein. In order to minimizethe actual height of the transfer zone, it is advantageous to provide itwith one or more devices for changing direction of flow. Erosion due tothe flow of highvelocity eroding suspensions through the transfer zoneis preferably minimized by an internal erosion resistant lining, whichserves as the primary protection for the metal structure. However,erosion will usually be a maximum in the aforementioned devices, andcare should be exercised in their design. It has been found that sucherosion can be reduced substantially if the changes of direction of floware about right-angled, e.g., a vertical straight portion of thetransfer zone is closely followed by a horizontal straight portion, andif such portions are connected by appropriately designed devices. Thesedevices function well when the aforementioned angle is between about 75and 105. One suitable design for such a connection is a so-calledside-out straight tee, i.e., a tee used as elbow, entering run. The farend of the run is capped and is thus closed to flow. A more preferreddesign, however, is comprised of a truncated hollow cone, advantageouslyan oblique cone, extending from one such portion of the transferconduit, the far end of the cone being its base of larger diameter, acap covering and closing said larger diameter base, and another suchportion of said transfer conduit extending from an outlet in the conicalsurface in such a way that the projected axes of the respective portionsof the transfer conduit are intersecting at angles in the range fromabout 75 to about 105 In a preferred embodiment of such a device, thereis provided between the base of the cone and the cap an extension suchas a hollow cylindrical extension of the same diameter as that of thebase. The inlet flow which enters through the smaller diameter area ofthe cone exits through the side outlet provided in the conical surface,such side outlet preferably having the same cross-sectional area as theinlet. The cone design has the advantage over the tee in that sharpedges at changes of direction, which are subject to erosion, have beenremoved from the direct line of impingement of a major portion of thesolids suspension. In both embodiments, the sudden change in directionof the high-velocity suspension causes solids to collect as a relativelydense suspension within the devices, especially in the respective closedportions thereof (i.e., in the far end of the run of the tee, or in thelarger diameter area of the cone or in the extension thereof), and saidcollected solids serve as a protective cushion on which the suspensionimpinges. The closed end portions of the aforementioned devices can beperiodically opened for inspection and maintenance purposes withoutnecessitating dismantling of any part of the transfer-reaction zone.

In addition, the primary structures forming these devices canadvantageously be enclosed within secondary protective structures ofsuitable designs, e.g., offset cylinders, where the annular spacebetween a device and its corresponding secondary protective structuremay be filled with an erosion resistant refractory material. Thus, incase of an actual erosion failure in the primary structure forming thedevice, the secondary protective structure will continue to maintain thesuspension within the transfer zone. Plant operations need not bedisrupted due to an erosion failure of the primary device, but can becontinued for relatively long periods of time before plant shutdown formaintenance becomes necessary. It is to be understood that any otherlocalized area of the transfer zone found to be subject to severeerosion could also be enclosed within secondary protective structuressimilar to the ones previously described.

More than one standpipe can be included in the design of the apparatusof this invention, each of these standpipes communicating with a sealwell with at least one transfer zone depending therefrom, i.e., thescope of the invention includes designs where two or more transfer zonesdepend from a common seal well. Such designs are useful in the efficientutilization of the space available in a relatively small lower vessel.I-IOwever, the preferred means for the conversion of dissimilarhydrocarbon feeds to be treated at different operating conditions is inseparate transfer-reaction zones depending from separate seal wells.

In a system comprised of one standpipe, one seal well and onetransfer-reaction zone, the desired temperature of a transfer-reactionzone is maintained by providing it with a temperature controller whichpreferably is located near the outlet of the transfer-reactor, and whichactuates the valve controlling the flow of hot regenerated catalystthrough the corresponding standpipe. As the temperature drops below adesired level, the valve is opened to increase the amount of catalyst tobe circulated and vice versa. In a system where one standpipe and oneseal well serve more than one transfer-reaction zone, the temperaturecontroller which actuates the catalyst flow valve is preferably locatedin the common disengaging zone in the lower vessel.

The outlet of the confined transfer zone or zones is located within thelower vessel and consequently is in open pressure communication with itscorresponding open seal well. The location of said outlets can either bewithin an upper portion of a stripping zone, or at points adjacentthereto, in which latter cases the stripping zone is advantageouslyprovided with solids inlet means e.g., in the form of slots in thestripping zone walls in the case of an internal stripper or with asolids control valve in the case of an external stripper. Generally,where the lower vessel contains a fluidized dense bed of solids, theoutlet should be positioned above the dense bed to minimize overcrackingof the hydrocarbons and to promote the rapid separation of the crackedvapors from the spent catalyst in the disengaging space provided by thevapor space of the lower vessel. It has been found that a furtherimprovement in the separation is obtained by providing the outletportion of the transfer zone with one or more side-dischargedistributing apertures or slots as compared with a simple bottom outlet.Furthermore, it is possible by a suitable arrangement of such slots toguide the flow of separated solids in a desired direction and therebyaid in the distribution of such solids. The use of the discharge slotsis not limited to disperse phase catalytic cracking zones, but appliesgenerally to any system for transport of gas-solids suspensions and thesubsequent separation, guidance and distribution of such solids.

The stripping zone can be of any suitable design and should includemeans for introducing stripping gas to a bottom portion thereofandpreferably baffles to increase the contact between stripping gas andsolids.

The apparatus should also include one or more riser conduits extendingfrom a lower portion of the stripping zone into the upper vessel whichserves as a regeneration zone, and said risers should be provided withinlets for lift gas to accomplish the upwards transport of solidsthrough said risers.

The operation of the apparatus will be described with reference to onestandpipe, one seal well enclosing said standpipe and onetransfer-reaction zone. However, it is understood that there can beplurality of standpipes, each having its corresponding seal well and oneor more transfer-reaction zones depending therefrom. Thus, hot freshlyregenerated catalyst in amounts controlled by the temperature-actuatedvalve is transferred from the upper vessel serving as a regenerationzone through a standpipe into a corresponding seal well located withinthe lower vessel and is subsequently introduced into a confinedtransfer-reaction zone at least a portion thereof being located outsidethe lower vessel. The catalyst is preferably aerated to maintain it in afluidized state while flowing through said standpipe. A dense fluidizedbed of such regenerated catalyst is maintained in the seal wellextending upwards into the annular space formed by the standpipe and thecorresponding seal well structure. The height of the sealing bed isdependent on the pressure drop through the transfer-reaction zone andwill fluctuate as the hydrocarbon feed rate, catalyst-to-oil ratio,temperature and pressure are varied. Being in a fluidized state, thesealing bed will act as a pressure-developing column and will provideprecisely the necessary pressure for transport of the catalyst throughthe subsequent reaction zone and any subsequent dense-bed reaction zonewhich may be superimposed on the transfer-reaction zone.

Hydrocarbon feed, preferably preheated, is introduced to the transferzone where it is contacted with the hot regenerated catalyst flowingtherethrough. The contact causes the formation of a dilute phasesuspension of catalyst and oil vapors, which moves through the confinedtransfer zone at high superficial velocities while cracking of thehydrocarbons is taking place. In a preferred embodiment, a densefluidized bed of regenerated catalyst is maintained in the first portionof the transfer zone upstream from the hydrocarbon feed inlet, said bedserving as a reverse pressure seal to prevent hydrocarbon vapors fromentering the open seal well in the event of a pressure upset in thesystem. The hydrocarbon feed can be fresh feed alone or a mixture offresh feed and recycle gas oil, recovered from subsequent producttreatment zones. In the cases where more than one transfer-reaction zoneis employed, dissimilar feeds which require different operatingconditions for optimum results, can be treated separately in what isgenerally called segregated feed cracking, e.g., the fresh hydrocarbonfeed and the recycle stream can be cracked in two separate zones.Examples of suitable feeds for treatment in the apparatus of theinvention include gas oils, reduced crudes, waxy feeds, etc.

A suspension of cracked hydrocarbons and catalyst exits from thetransfer-reaction zone and is advantageously withdrawn therefrom throughone or more apertures or slots to promote rapid disengagement of spentcatalyst. The spent catalyst exiting from the reaction zone isdischarged above a dense fluidized bed of catalyst which is maintainedin a bottom portion of the lower vessel. In one embodiment, said latterbed may serve as a true reaction zone by the additional introduction ofa stream of hydrocarbons to said bed, and such an arrangement can beused with advantage for converting a hydrocarbon stream which isrelatively hard to crack, e.g., a cycle oil which would requirerelatively longer times for its conversion into lower boiling material.

In another embodiment, no additional hydrocarbons are fed to theaforementioned dense bed, which in this case will serve as at least afirst stripping zone. In one specific aspect, the spent catalyst iscontacted in such bed with a sufficient quantity of a gaseous material,such as steam or nitrogen, to maintain the bed in a turbulent densestate of such dimensions that there is provided adequate time to stripoff the vaporizable hydrocarbons from the catalyst particles. ln anotherspecific aspect, only such quantity of gaseous material is provided tothe bed to assure the fluidized movement of particles therein. In thiscase, the bed performs very little stripping duty but serves mainly as asupport much like a baffle to guide the disengaged and rapidly movingspent catalyst from the transferreaction zone into a separate andconfined stripping zone located within said lower vessel.

The effluents from the stripping zone and from the reaction zone arepreferably combined and subsequently separated from entrained catalystparticles by means of cyclones located in an upper portion of the lowervessel and are thereafter transferred to conventional product treatmentzones including fractionation zones for recovery of normally gaseoushydrocarbon products, gasolines product and higher boiling fractions,which can include light and heavy fuel oil fractions and/or recycle gasoil fractions, the latter to be returned to the reaction zone or zonesfor further cracking.

The stripped catalyst is transported through one or more riser conduitsinto the upper vessel, where it is regenerated by burning thecarbonaceous deposits on the catalyst in an oxygen-containingatmosphere. The transport and regeneration is carried out in anyconventional manner and should preferably include use of at least partof the oxygen-containing regeneration gas for elevating the strippedcatalyst to the regeneration zone.

The operating conditions employed to achieve catalytic cracking ofhydrocarbons according to the invention include regenerator temperaturesbetween about l,l00 F. and about l,500 F. and regenerator dilute phasepressures from about atmospheric pressure to about 35 p.s.i.g. Thedensity of the sealing bed in the seal well structure, is preferablymaintained at values ranging from 20 lb./cu.ft. to about 45 lb.lcu.ft.The same range applies to preferred densities of the bed of regeneratedcatalyst maintained within the first portion of the transfer zone, whichgenerate the reverse pressure seal. The outlet of the disperse phasereaction zone can be operated in a temperature range above 850 F. andpreferably between about 925 F. and about l,000 F. Suitable reactionzone pressures are between about 5 p.s.i.g. and 50 p.s.i.g. The relativeweights of catalyst and total hydrocarbons flowing through the elongatedconfined reaction zone, i.e., the so-called catalyst to oil ratio, ispreferably maintained at values ranging between about 2 and about 20.The length and volume of the elongated reaction zone should besufficient to provide contact times therein from about 0.5 second toabout 4 seconds or even higher, while the cross-sectional area of saidzone is designed to result in superficial velocities of the suspensionranging between about 15 ft./sec. and about 25 ft./sec. in the vicinityof the hydrocarbon feed inlet and between about 20 ftjsec. and about 60ft./sec. at the reactor outlet. In those cases where additionalhydrocarbon feed is introduced to the dense bed located in a bottomportion of the lower vessel, the conditions for this portion of thereaction include, in addition to the above-cited reaction temperaturesand pressures, catalyst/oil ratios ranging between about 2 and about 25,preferably between about 5 and 10, and space velocities, i.e., thehourly weight of hydrocarbons fed to the dense bed divided by the weightof said bed, ranging between about 0.25 and I5 and preferably from about0.5 to about 5.

In the embodiments where no additional hydrocarbon feed is introduced tothe bed maintained in the lower portion of the lower vessel, and wheresaid bed functions mainly as means for directing the flow of spentcatalyst into a main stripping zone, the superficial velocity of thefluidizing agent in said bed, such as steam or nitrogen, is preferablymaintained in a range from about 0.04 ft./sec. to about 0.2 ft./sec.

The operating conditions employed in the stripping of spent catalyst ina stripping zone includes temperatures above about 825 F and preferablybetween about 900 F. and about 975 F., and pressures ranging betweenabout 10 p.s.i.g. and about 55 p.s.i.g. The amount of stripping mediumrelative to the catalyst circulation is advantageously maintainedbetween about 1 and about l0 pounds per 1,000 pounds of circulatedcatalyst. Superficial velocities of the stripping medium are from about0.5 ft./sec. to about 2.0 ft./sec.

in order to provide a better understanding of the present invention,reference will be had to the accompanying schematic drawings which forma part of this specification.

In the drawings:

FIG. 1 is an elevated view of a specific example of the apparatus of theinvention, which includes two separate standpipe-open seal well-transferconduit systems, only one of said systems being shown. In this examplethe lower vessel is of sufficient size to accommodate a major portion ofeach transfer conduit.

FIG. 2 is a sectional view taken on line AA of the FIG. 1 lookingdownward.

FIG. 3 is a specific example of a device for changing the direction offlow of an erosive disperse phase suspension.

FIG. 4 is an elevated view of another specific example of the apparatusof the invention wherein a large portion of the transfer zone is locatedoutside the lower vessel.

FIG. 5 is a sectional view taken on line B-B of the FIG. 4 lookingdownward.

It is to be understood that the drawings are only shown in sufficientdetail to fully understand the invention and that some portions of thesystem such as the fluidized dense bed regenerator as well as reactioneffluent outlets and subsequent product recovery zone have not beenincluded since those employed are conventional.

The apparatus shown in FIGS. 1 and 2 is a single-head" system comprisingan upper vessel 1 containing a regenerator zone (only partially shown inFIG. 1), which is superimposed on and vertically aligned with a lowervessel 2. Two vertical standpipes 3, which are supported by thepartition 4, extend downwardly into open seal well structures 6, whichare supported by the bottom of the lower vessel 2. The standpipes andtheir respective open seal wells are located 180 F. apart in the spaceprovided between the central cylindrical stripping zone 7 and the wallsof vessel 2. The steady flow of freshly regenerated catalyst through thestandpipe, which is aided by the introduction of aeration gasesthroughout the heights of the standpipes (not shown on the drawing), iscontrolled by plug valves 8. The catalyst flows into open seal wells 6,where fluidized dense beds of such material are maintained and whichextend upwards in the annular spaces 9. The fluidization of said beds isaccomplished by the introduction of aeration steam through distributorrings 11 and 12. The bottom portion 10 of each seal well is partitionedinto two sections 13 and 14 by means of vertical baffle 16. Thesebaffles serve to reverse the direction of flow of high-velocity densephase catalyst issuing downwardly out of the standpipes, resulting inlow-velocity upward flowing dense phase suspensions in sections 13. Saidsuspensions then flow over the respective baffles into the secondaerated sections 14 of the seal wells. Subsequently the catalyst flowsinto the first external sections 17 of the transfer-reaction conduits,said first sections originating within the seal wells and depending in adownward direction from the second aerated sections of the open sealwells. Aeration gases are introduced (not shown) throughout the lengthof the external section of the transfer zone to aid the flow of catalysttherethrough. A change of direction of the flow of catalyst is obtainedby means of bend 18, and the catalyst proceeds in a lateral and upwarddirection through section 19 equipped with aeration gas nozzles 21 tomaintain therein fluidized dense bed reverse pressure seals. Steamnozzles 22 are provided for the injection of emergency steam in case ofloss of hydrocarbon feed and for introduction of steam to maintaincatalyst flow during startup and shutdown. Hydrocarbon feed isintroduced by means of an injection nozzle 23, introducing thehydrocarbon vertically into riser conduit 24 contained within the lowervessel. The resulting dilute suspensions of vaporized hydrocarbons andcatalyst flow through the vertical riser portions 24 of thetransfer-reaction zones, into the crossover portions 26 and subsequentlyinto vertical downcomer portions 27 provided with discharge slots 28.The respective riser-crossover and crossover-downcomer portions areconnected by means of side out tees, which are provided with caps 31 atthe far ends of their respective runs. All internal metal surfaces ofthese devices for changing the direction of flow and all connectingconduits thereto, are lined with an erosion resistant refractory. Thedevices are shielded by the secondary protective structures 32, theannuli formed thereby being filled with erosion resistance refractorymaterial, if desired. The downcomers are closed below the dischargeslots by means of plates 33 and are supported in the example byextensions 34 attached to the bottom of vessel 2. However, other methodsfor closing and support of the transfer conduit can be employed. Abarely fluidized dense bed 36 of catalyst is maintained in the bottomportion of the lower vessel 2 and fluidization is maintained by theintroduction of steam through the aeration ring 37. The crackedvapor-catalyst suspensions which exit through the discharge slots arerapidly disengaged in the vapor space above bed 38 and the separatedcatalyst particles are guided along the surface bed 36 into stripperinlet slots 39, where they are contacted with stripping steam providedthrough distribution rings 41. The stripped catalyst is transported toregeneration zone 1 by means of riser 42 with the lift gas beingprovided through hollow plug valve 43. The disengaged cracked vaporsemanating from discharge slots 28 are combined with the vaporousstripper effluent from stripping zone 7 and subsequently passed tocyclones (not shown) for recovery of entrained catalyst therein. Thevapors then exit from (not shown) the lower vessel and are passed toproduct recovery zones including fractionation zones (not shown).

With the apparatus of FIGS. 1 and 2 it is possible to achieve at least a25 per cent increase in either contact time or hydrocarbon feedthroughput as compared with the apparatus of application Ser. No.719,052 FIGS. 1 and 2, wherein the transfer-reaction zone is totallyenclosed within the lower vessel. Furthermore, there are few maintenanceproblems associated with the apparatus of this invention by reason ofthe external locations of many of the aeration gas nozzles andhydrocarbon feed inlet nozzles thus providing easy access thereto ifneeded.

FIG. 3 depicts an alternate device to a side out" tee employed forchanging the direction of the flow of an erosive solids suspension, suchas, for instance, the disperse phase hydrocarbon vapor-catalystsuspension in conduits 24, 26 and 27 of FIG. 1. This device is describedhereinafter with respect to its connection to a vertical riser conduit52 and a horizontal crossover conduit 53; however, it can equally wellbe employed to connect a horizontal crossover with a subsequent verticaldowncomer. The device is comprised of a truncated oblique cone, which isconnected at its lesser diameter section to riser conduit 52 and at itsoblique surface to the crossover section. A cylindrical extension 54 isprovided at the larger diameter area of the cone which is capped bymeans of plate 56 or alternatively by other suitable closures such as adished or ellipsoidal head. All internal metal surfaces of the conedevice, as well as of all connecting conduits are lined with anerosion-resistant refractory material 57, serving as primary protectiontherefor. A secondary protection is obtained by the enclosure of thedevice within a cylindrical structure 58, which is filled withadditional erosion-resistant refractory material 59. The high-velocityupflowing solids-suspension from riser 52 causes solids to be collectedand held in relatively dense suspension within the portion of the deviceextending above crossover conduit 53, and said solids act as a furtherprotection against erosion in this area as the high-velocity suspensionimpinges thereon. The advantage of the device of FIG. 3 over the sideout" tees in FIGS. 1 and 2 lies primarily in the removal of sharpprojections 61 and 62 from the direct line of travel of thehigh-velocity eroding suspension and thereby considerably reducingerosion at such projections.

The apparatus shown in FIGS. 4 and 5 is a two-head" system wherein amajor portion of the transfer zone, including the vertical riser, thecrossover portion and part of the downcomer, is located outside thelower vessel. In other respects the apparatus is substantially identicalto the one depicted in FIGS. 1 and 2. For simplicity, the description ofthe features common to both apparatuses have herein been omitted, thenumbering of such details being the same as in FIGS. 1 and 2.

The upwardly sloping lateral sections 19 are connected to extemalvertical risers 71 by means of the vertical sections 72.

Expansion joints (not shown) can be provided if required to preventmechanical failure of the transfer conduit system due to expansion orcontraction during startup and shutdown periods. Hydrocarbon feed isintroduced by means of nozzles 73 into external risers 71, which extendto a height above that of the lower vessel 2 but below the upperregenerator vessel (not shown on the drawing). The resulting suspensionsof vaporized hydrocarbons and catalyst flow through the risers, into theexternal crossover portions 74 and subsequently into vertical downcomerportions 76. The first sections of said downcomers are located outsidethe lower vessel. Steam for startup and emergency use is introduced vianozzle 77. Hollow oblique cones 78 having caps 79 connect the riser,crossover and downcomer sections.

With this apparatus design it is possible to achieve any desired contacttimes and hydrocarbon feed rates, since the lower vessel is onlyrequired to house the outlet portions of the transfer zones and the sealwells. The appurtenant equipment such as strippers and cyclones could,if desired, be located externally to the lower vessel.

It is evident that there are many other possible modifications to theapparatus of the invention. For instance, the transfer line zone couldinclude an external vertical riser portion, a partially externalcrossover portion and an internal downcomer portion, the crossoverportion then entering the side of the lower vessel.

Also, it is not necessary when at least two transfer zones are employed,that they be of the same size and configuration, which is particularlythe case when dissimilar hydrocarbon feeds are cracked in the apparatus.

What is claimed is:

1. An apparatus for the conversion of hydrocarbons, which comprises:

an upper vessel;

a lower vessel;

a structure forming an open seal well supported by said lower vessel;

a standpipe in communication with the upper vessel and the open sealwell;

a confined elongated transfer zone depending from said seal well andpartially located outside said lower vessel and having the outletportion located within said lower vessel in open pressure communicationwith said seal well;

valve means for controlling flow of solid material through saidstandpipe into said seal well;

means for introducing hydrocarbon feed into the confined elongatedtransfer zone;

a solids stripping zone;

means for introducing solids from the transfer zone into said strippingzone, and

means for transferring solids from the solids stripping zone to theupper vessel.

2. An apparatus according to claim 1 wherein a bottom portion of saidwell is provided with fluidizing gas inlet means.

3. An apparatus according to claim 1 in which a vertical baftie isprovided in the lower portion of the open sea] well structure, dividingsaid structure into two sections.

4. An apparatus according to claim 1 wherein means are provided tomaintain a reverse pressure seal within a first portion of saidelongated transfer zone and wherein the hydrocarbon inlet means arelocated downstream from said reverse pressure seal.

5. An apparatus according to claim 1 wherein a last portion of saidtransfer zone is an apertured conduit.

6. An apparatus according to claim 1 wherein said valve means is atemperature actuated plug valve located at the outlet from the standpipeand responsive to temperature fluctuations within the transfer zone.

7. An apparatus according to claim 1 wherein fluidizing medium inletmeans are provided in a bottom portion of said lower vessel.

8. An apparatus according to claim 4 wherein means are provided forintroducing fluidizing gas to said first portion of the transfer zone.

9. An apparatus according to claim 4 in which the first portion of saidtransfer zone is comprised of a conduit forming about a bend, one legthereof depending downwardly from said seal well.

10. An apparatus according to claim 4 in which the first portion of saidtransfer zone is comprised of a first section depending from said sealwell and extending downwardly therefrom, a second section forming a bendand a third upwardly sloping lateral section.

11. An apparatus according to claim 4 wherein a second portion of saidtransfer zone is a substantially vertical riser conduit.

12. An apparatus according to claim 5 wherein the stripping zone islocated within the lower vessel adjacent to said last portion of thetransfer zone.

13. An apparatus according to claim 10 wherein said second section ofthe first portion of the transfer zone is a short radius bend.

14. An apparatus according to claim 11 in which the transfer conduit iscomprised of the following additional portions:

a first device for changing the direction of flow of material exitingthe second substantially vertical riser portion;

a third and substantially horizontal crossover portion;

a second device for changing the direction of flow of material exitingthe third portion, and

a fourth and substantially vertical downcomer portion.

15. An apparatus according to claim 14 in which said devices arespatially enclosed within protective structures.

16. An apparatus according to claim 14 in which the vertical riserportion is located outside the lower vessel.

17. An apparatus according to claim 15 wherein the spaces between saiddevices and their respective protective structures are filled with anerosion-resistant refractory material.

18. An apparatus according to claim 16 in which the horizontal crossoverportion is located at least partially outside the lower vessel.

19. An apparatus for the conversion of hydrocarbons which comprises:

an upper vessel;

a lower vessel disposed in vertical alignment with said upper vessel;

a structure forming an open seal well within said lower vessel andrigidly supported by a bottom portion of said lower vessel;

a suspended vertical standpipe in communication with the upper and thelower vessels and extending downwardly into the open seal well;

a plug valve located at the outlet from the vertical standpipe forcontrol of flow therethrough;

first means for introducing a fluidizing medium into a bottom portion ofsaid well;

a confined elongated transfer zone depending from said seal well andpartially located outside said lower vessel and having the outletportion located within said lower vessel in open pressure communicationwith said seal well;

second means for introducing a fluidizing medium into said first portionof the transfer zone;

at least one hydrocarbon feed inlet to said transfer zone downstreamfrom said second fluidizing medium inlet means;

a solids stripping zone;

means for introducing solids from the transfer zone into the strippingzone, and

at least one riser conduit for the transfer of solids from the strippingzone to the upper vessel.

20. A method for the conversion of hydrocarbons comprising:

transferring hot, freshly regenerated catalyst of fluidizable particlesize from an upper regeneration zone through a standpipe to an open sealwell supported by a lower vessel;

maintaining said open seal well in open pressure communication with theoutlet of a confined elongated transfer zone, said transfer zonedepending from said seal well and being located partially outside thelower vessel;

maintaining a sealing and pressure-developing dense bed of peraturesabove those employed in the transfer zone.

21. A method according to claim 20 wherein a reverse pressure sealcomprised of a second dense fluidized bed of regenerated catalyst ismaintained in a first portion of the elongated confined transfer zone.

22. A method according to claim 20 wherein two transfer zones areemployed and wherein dissimilar hydrocarbon feeds are contacted withcatalyst in the respective transfer zones.

23. A method according to claim 20 wherein a dense fluidized bed ofcatalyst is maintained in a bottom portion of the lower vessel.

24. A method according to claim 20 wherein the cracked hydrocarbons andspent catalyst are withdrawn through discharge slots provided in saidoutlet portion.

25. A method according to claim 23 wherein a second hydrocarbon feed iscontacted with said dense fluidized bed within the bottom portion of thelower vessel under conditions suitable for cracking of said secondhydrocarbon feed.

2. An apparatus according to claim 1 wherein a bottom portion of saidwell is provided with fluidizing gas inlet means.
 3. An apparatusaccording to claim 1 in which a vertical baffle is provided in the lowerportion of the open seal well structure, dividing said structure intotwo sections.
 4. An apparatus according to claim 1 wherein means areprovided to maintain a reverse pressure seal within a first portion ofsaid elongated transfer zone and wherein the hydrocarbon inlet means arelocated downstream from said reverse pressure seal.
 5. An apparatusaccording to claim 1 wherein a last portion of said transfer zone is anapertured conduit.
 6. An apparatus according to claim 1 wherein saidvalve means is a temperature actuated plug valve located at the outletfrom the standpipe and responsive to temperature fluctuations within thetransfer zone.
 7. An apparatus according to claim 1 wherein fluidizingmedium inlet means are provided in a bottom portion of said lowervessel.
 8. AN apparatus according to claim 4 wherein means are providedfor introducing fluidizing gas to said first portion of the transferzone.
 9. An apparatus according to claim 4 in which the first portion ofsaid transfer zone is comprised of a conduit forming about a 180* bend,one leg thereof depending downwardly from said seal well.
 10. Anapparatus according to claim 4 in which the first portion of saidtransfer zone is comprised of a first section depending from said sealwell and extending downwardly therefrom, a second section forming a bendand a third upwardly sloping lateral section.
 11. An apparatus accordingto claim 4 wherein a second portion of said transfer zone is asubstantially vertical riser conduit.
 12. An apparatus according toclaim 5 wherein the stripping zone is located within the lower vesseladjacent to said last portion of the transfer zone.
 13. An apparatusaccording to claim 10 wherein said second section of the first portionof the transfer zone is a short radius bend.
 14. An apparatus accordingto claim 11 in which the transfer conduit is comprised of the followingadditional portions: a first device for changing the direction of flowof material exiting the second substantially vertical riser portion; athird and substantially horizontal crossover portion; a second devicefor changing the direction of flow of material exiting the thirdportion, and a fourth and substantially vertical downcomer portion. 15.An apparatus according to claim 14 in which said devices are spatiallyenclosed within protective structures.
 16. An apparatus according toclaim 14 in which the vertical riser portion is located outside thelower vessel.
 17. An apparatus according to claim 15 wherein the spacesbetween said devices and their respective protective structures arefilled with an erosion-resistant refractory material.
 18. An apparatusaccording to claim 16 in which the horizontal crossover portion islocated at least partially outside the lower vessel.
 19. An apparatusfor the conversion of hydrocarbons which comprises: an upper vessel; alower vessel disposed in vertical alignment with said upper vessel; astructure forming an open seal well within said lower vessel and rigidlysupported by a bottom portion of said lower vessel; a suspended verticalstandpipe in communication with the upper and the lower vessels andextending downwardly into the open seal well; a plug valve located atthe outlet from the vertical standpipe for control of flow therethrough;first means for introducing a fluidizing medium into a bottom portion ofsaid well; a confined elongated transfer zone depending from said sealwell and partially located outside said lower vessel and having theoutlet portion located within said lower vessel in open pressurecommunication with said seal well; second means for introducing afluidizing medium into said first portion of the transfer zone; at leastone hydrocarbon feed inlet to said transfer zone downstream from saidsecond fluidizing medium inlet means; a solids stripping zone; means forintroducing solids from the transfer zone into the stripping zone, andat least one riser conduit for the transfer of solids from the strippingzone to the upper vessel.
 20. A method for the conversion ofhydrocarbons comprising: transferring hot, freshly regenerated catalystof fluidizable particle size from an upper regeneration zone through astandpipe to an open seal well supported by a lower vessel; maintainingsaid open seal well in open pressure communication with the outlet of aconfined elongated transfer zone, said transfer zone depending from saidseal well and being located partially outside the lower vessel;maintaining a sealing and pressure-developing dense bed of fluidized,regenerated catalyst in said open seal well; employing the thusdeveloped pressure for transferring catalyst from said open seal wEllthrough said confined elongated transfer zone; concurrently contactingin said transfer zone said catalyst with hydrocarbon feed underconditions suitable for cracking of said hydrocarbon feed; withdrawingcracked hydrocarbons and spent catalyst from the outlet portion of thetransfer zone; stripping spent catalyst of strippable hydrocarbons in astripping zone; recovering cracked and strippable hydrocarbons in aproduct recovery zone, and regenerating stripped catalyst in the upperregeneration zone by contact with an oxygen-containing gas attemperatures above those employed in the transfer zone.
 21. A methodaccording to claim 20 wherein a reverse pressure seal comprised of asecond dense fluidized bed of regenerated catalyst is maintained in afirst portion of the elongated confined transfer zone.
 22. A methodaccording to claim 20 wherein two transfer zones are employed andwherein dissimilar hydrocarbon feeds are contacted with catalyst in therespective transfer zones.
 23. A method according to claim 20 wherein adense fluidized bed of catalyst is maintained in a bottom portion of thelower vessel.
 24. A method according to claim 20 wherein the crackedhydrocarbons and spent catalyst are withdrawn through discharge slotsprovided in said outlet portion.
 25. A method according to claim 23wherein a second hydrocarbon feed is contacted with said dense fluidizedbed within the bottom portion of the lower vessel under conditionssuitable for cracking of said second hydrocarbon feed.